The invention refers to a lighting apparatus having a batwing type of distribution of the luminous flux, the light source of which may be constituted by fluorescent tubes or by a discharge bulb.
The different studies made during recent years about reflected glare and direct glare, that is, about "Veiling Reflections" and "Discomfort Glare", have resulted in similar conclusions that are revealed by the candlepower distribution of some luminaires, which are intended to obtain a maximum candlepower in the 40.degree.-45.degree. zone from nadir with candlepower at nadir being ideally as low as possible.
Summing up, in a vertical cross plan of a luminaire with fluorescent lamps or with a discharge bulb, it is desired to have a minimum light distribution under 30.degree., a maximum light distribution between 40.degree. and 50.degree., and a minimum over 60.degree., because over 60.degree. discomfort glare takes place, and under 30.degree. veiling reflection takes place. This type of distribution is known as "batwing distribution".
In my previous patent No. 3,866,036 an optical device is described to obtain a batwing type of illumination in lighting apparatus fitted with fluorescent tubes, such device including strips of transparent material with an even and smooth face, an opposite face provided with triangular longitudinal prisms the top edges of which are cut off and replaced by rectangular prismatic portions with their free surfaces opaque or opal, each one of said strips being placed beneath each fluorescent tube of the lighting apparatus with their prismatic face directed towards the tube. The light rays the direction of which is near to the vertical are intercepted by the opaque or opal surfaces or are diverted laterally by the triangular prisms, the device thus giving a batwing illumination.
I have found that the light distribution and the output of such device may be improved by placing the lighting source and the optical device in a housing having a suitable configuration resulting in a lighting apparatus that fulfills the IES recommendations for the most efficient use of energy, that is, limiting the glare lumens and obtaining the maximum visibility lumens, such result being accomplished by using either fluorescent lamps or discharge bulbs as lighting sources.